Fix atan2 dimension bug; add atan2 tests

Author: imacg

src/Data/Quantity/Math.purs

@@ -42,7 +42,7 @@ import Data.Foldable (foldM)
 import Data.Decimal (Decimal)
 import Data.Either (Either)
 import Data.Quantity (Quantity, ConversionError, derivedUnit, asValueIn',
-                      scalar', quantity', toScalar', (⊘), (⊕))
+                      scalar', quantity', toScalar', (⊘), (⊕), (.*))
 
 type Result = Either ConversionError Quantity
 
@@ -66,7 +66,9 @@ atan ∷ Quantity → Result
 atan = lift Decimal.atan
 
 atan2 ∷ Quantity → Quantity → Result
-atan2 = lift2 Decimal.atan2
+atan2 x y = removeDims <$> lift2 Decimal.atan2 x y
+  where
+    removeDims q = q ⊘ 1.0 .* derivedUnit q
 
 cos ∷ Quantity → Result
 cos = lift Decimal.cos

test/Main.purs

@@ -33,7 +33,7 @@ import Data.Quantity (Quantity, (.*), prettyPrint, (⊕), (⊖), (⊗), (⊘),
                       errorMessage, showResult, qNegate, isFinite,
                       ConversionError(..))
 import Data.Quantity as Q
-import Data.Quantity.Math (sin, asin, pi, modulo, max, min, mean)
+import Data.Quantity.Math (sin, asin, pi, modulo, max, min, mean, atan2)
 
 import Control.Monad.Eff (Eff)
 import Control.Monad.Eff.Console (CONSOLE)
@@ -486,6 +486,11 @@ main = runTest do
       equal (Right $ 0.04 .* meter) ((2.0 .* meter) `modulo` (7.0 .* centi meter))
       equal (Left (ConversionError second meter)) ((8.0 .* meter) `modulo` (5.0 .* seconds))
 
+    test "atan2" do
+      almostEqual' (scalar (Math.pi / 2.0)) ((scalar 10.0) `atan2` (scalar 0.0))
+      almostEqual' (scalar (Math.pi / 4.0)) ((100.0 .* centi meter) `atan2` (1.0 .* meter))
+      equal (Left (ConversionError meter second)) ((1.0 .* second) `atan2` (2.0 .* meter))
+
     let qs1 = NonEmptyList $ scalar (-3.0) :| scalar 4.0 : scalar 2.0 : Nil
     let qs2 = NonEmptyList $  (300.0 .* centi meter)
                            :| (0.0254 .* meter)